I've just been reading the blog of Phenderson Djeli Clark, at pdjeliclark.wordpress.com. On 11th September she was talking about her experiences of trying to get her novel published - an Egypto-Nubian fantasy with a word count that enabled it to be split into four separate novels, and with a lot of black female characters - the Daughters of Sekhmet sound like fun!
I sympathise greatly with her struggles with agents and publishers - but one of the reasons that was suggested for why the book was not taken up was that it was a portal fantasy.
Now, I spent many hours as a child sitting in my mother's wardrobe trying to get to Narnia, so I'm naturally in favour of portals to other worlds. That's why my own first attempts at serious fantasy involve portals. Some of my characters live in Hay-on-Wye, the secondhand booktown on the Welsh Borders (on the grounds of 'write what you know', as I've been working in bookshops in Hay-on-Wye for around twenty years now), but they have a whole other life in the fantasy world of Ytir - one that they're reluctant to return to, for various very good reasons.
Like Phenderson Djeli Clark, I toyed with the idea of setting my story wholly within the fantasy world, which involved a huge amount of re-writing - but in the end, I decided I wanted the Hay-on-Wye parts of it, dammit, and I was going to have them. Which involved even more re-writing to get it back to the shape it had before (though I hope rather better written after all that work!).* And, despite the kind rejection letters that told me I was almost there as far as professional publishing was concerned, I decided I wasn't getting any younger and I wanted the stories to be out there and available - which is why I went the Smashwords route.
She's had some supportive comments about the portals, so maybe they're not the liability they're thought to be.
*as David Gerrold once said: "Remember, the first million words are just for practice!"